The family of sodipotassic copper tube silicates of the general formula Na.sub.2-2x K.sub.2x CuSi.sub.4 Ohd 10 (where x is equal to 0, 1/2, or 1) has three distinct species--these being, a sodium end of the formula Na.sub.2 CuSi.sub.4 O.sub.10 (sometimes referred to as the .alpha. phase), a potassium end of the formula K.sub.2 CuSi.sub.4 O.sub.10 (sometimes referred to as the .beta. phase), and an intermediate phase, litidionite (NaKCuSi.sub.4 O.sub.10). Of these, litidionite exists in nature (but is even then rare), whereas the .alpha. and .beta. phases must be synthesized. These sodipotassic copper tube silicates are, in general, comprised of an interconnecting network of Si-O bonds forming long tubes with a high aspect ratio. In this regard, please see Kawamura et al, Bull. Mineral 104, 387-395 (1981), the entire content of which is expressly incorporated hereinto by reference.
Synthesis of all three species of sodipotassic copper tube silicates has been proposed in the past. However, the typical synthesis route for forming these sodipotassic copper tube silicates generally includes melt processing of the reagents. More specifically, sodipotassic copper tube silicates have been synthesized in the past by a technique commonly referred to as "devitrification". This prior technique includes melting oxides of the reagents, pulverizing the cooled melt, followed by annealing over a bed of crystalline litidionite supported by a quartz plate. The product was then typically repulverized and calcined for homogeneity. See generally, Hefter et al, "Synthesis of the Tube Silicate Litidionite and Structural Relationships between It and Some Other Silicates", Inorg. Chem. 21, 2810-2816 (1982).
Sodipotassic copper tube silicates may be usefully employed, for example, as reinforcing media (e.g., due to the silicates' excellent stiffness) so as to form composites with polymers, preceramic and ceramic materials. However, the conventional techniques employed to synthesize these sodipotassic copper tube silicates is not commercially viable since the melt-processing of the oxide reagents is energy intensive. Furthermore, conventional processes require sintering at high temperatures for several days (often for twenty-one days or longer). These constraints imposed by conventional processing techniques are therefore not conducive to producing sodipotassic copper tube silicates on an economically commercial scale.
It is towards providing a commercially viable synthesis route to sodipotassic copper tube silicates that the present invention is directed.
Thus, one aspect of the present invention is that sodipotassic copper tube silicates may be synthesized at relatively low temperatures without first melt processing the oxide reagents (as necessary according to conventional synthesis routes). More specifically, the present invention is concerned with synthesizing sodipotassic copper tube silicates by first forming (at essentially room temperature) a gel of the reagents, and then sintering the formed gel at elevated temperature and for a time sufficient to form crystalline sodipotassic copper tube silicates.
These aspects, and others, will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.